A conventional three-component die set for stamping sheet metal parts consists of a punch, a binder ring and a female die. Such die sets are used to make many strong and light weight articles of manufacture. These articles include, for example, automotive body panels and other structure parts; aircraft and appliance sheet components; and beverage cans. Families of formable ferrous and aluminum sheet metal alloys have been developed for these manufacturing processes.
In a typical sheet metal forming operation, a flat blank of the metal is held at its periphery over the shaped cavity surface of a female die and the sheet is pulled into the cavity and against the shaped surface using a punch with a forming surface complementary to that of the female die. The sheet is drawn and stretched between the tools and assumes a desired shape. In making stamped parts such as automotive body panels, often characterized by deep pockets and small radii bends, the panel may be formed in stages using two or more sets of stamping dies each operated in a suitable hydraulic press.
In sheet metal stamping operations the blank is clamped at its periphery against the marginal surface of the female die cavity with a blank holder called the binder ring. The interaction between the binder ring, the interposed sheet and the binder portion at the margin of the female die is critical to making a part that is formed free of wrinkles or tears. The binder ring has a bead that presses adjacent sheet metal into a complementary depression, a trough, in the binder portion of the female die to create proper restraining forces that prevent the sheet metal from being drawn to the die cavity too freely (and cause wrinkles on the sheet metal) or too restrictively (thus causing panel splits). Thus, a peripheral ring of the blank material is crimped and grasped by the binder ring system. When operation of the stamping press brings the punch into contact with the blank, the metal sheet is drawn and/or stretched into the forming cavity. The binder bead/trough interactions at each point around the entire periphery of the blank control the local amount of sheet metal drawn into the forming die. The draw-in of too little metal over the binder ring system can lead to tears or cracks in the stamped part, and too much drawn metal can lead to wrinkles and surface distortions. The draw-in amount is controlled by the die design and die construction, the forming process parameters (binder force, lubrication, die set-up), and the sheet metal properties.
In a traditional die development and making process, a die is designed based on previous experience, and the die is validated through a series of physical tryouts. These tryouts are time consuming and costly and cannot guarantee the success of the die developments. For a typical automotive body panel, say a fender, the tryout alone could last twelve months and cost more than one million U.S. dollars. Today in math-based die development practice, the design of a die can be evaluated and reshaped through electronic tryout via advanced stamping simulation technology that consists of stamping CAE (computer aided engineering) programs, sheet metal forming simulation software (e.g., Pamstamp™ and Dyna3D™) and high performance computers.
After the die sets for a vehicle body panel, for example, are designed or developed successfully in the digital world, the dies are constructed and tried out in a tooling shop. However, there are differences between the engineering of a die set and its everyday use in a manufacturing operation. And there are differences in results obtained between digital simulation of die operation and physical parts produced in a stamping plant. One aspect of the problem is that die makers are not so familiar with math-based die engineering principles that they can make good use of the math-based work in tuning actual dies for everyday stamping operations and ordinary sheet metal material. Therefore, physical tryout periods for each set of manufacturing dies can still take weeks or months because there has been no robust procedure by which manufacturing people can detect and correct differences between an actual die set and the math-based simulation from which it was built.
It is an object of this invention to provide a process for conforming actual sheet metal stamping experience using a specific die set with state-of-the-art math-based simulation of the die set and stamping operation. It is a more specific object of this invention to provide a process for using the exact amount of sheet metal drawn in over the binder ring at selected locations around the periphery of the blank as a practical and effective basis to conform the operation of the physical die set to the simulated performance of the virtual die set.